Lecture Eleven

Question 1

What is pressure?

Answer 1

Any object that strikes a surface and exerts a force against it. Ant temperature greater than 0K causes atoms/molecules to alway be in motion. Atoms/molecules exert force though collisions with each other and with the walls of their container. The collective result of these collisions is what we call pressure (P).

Question 2

What is Boyle’s Law?

Answer 2

PV = k. Pressure was originally measured using a manometer. Liquid mercury moves as the external pressure changes. Hence mmHg, i.e. millimetres of mercury.

P1V1 = P2V2

Question 3

What is Charles’s Law?

Answer 3

V ∝ T, i.e. volume is directly proportional to temperature. As a gas heats up, it expands.

Question 4

What is Avogadro’s Law?

Answer 4

As the number of moles of gas increases, the volume of the gas increases (at constant P and T). Note that pressure and temperature are not always constant, particularly in a reaction.

Question 5

What is the Ideal Gas Equation?

Answer 5

PV = nRT.

Question 6

How can density be derived using the ideal gas equation?

Answer 6

Density = m/v.

Therefore:

m/M = pV/RT –> m/v = pM/RT = density.

Note that: Density increases linearly with increasing P (@ a fixed T) - P is directly proportional with density.

Density decreases linearly with increasing T (@ a fixed P)

• Density is directly proportional with (1/T).

Density increases linearly with M (@ a fixed P and T)

• Density is directly proportional to M.